Filter for polymer processing and method of manufacture

ABSTRACT

A filter arrangement for a method of molten polymer processing is disclosed in which a plurality of filter elements are disposed in a filter cavity, with each element including filter surfaces aligned with the general direction of flow through the filter cavity, to thereby increase the effective filter surface area, and each element also including restrictive flow paths internally of the filter surface to maintain a relatively large pressure drop across the filter required for proper polymer processing in which conditioning of the molten polymer occurs to create long link molecules. The method of manufacture includes the steps of assembling a sandwich of outer layers of a filtering mesh and inner layers of a coarser mesh, diffusion bonding the layers together, sealing the edges, cutting the resulting sandwich in half by an electrodischarge, electron beam, laser machining, or other suitable process, pressing the open edge of each half into a respective opening in a manifold plate, and bonding each half thereto. In a preferred version of the process, the sealing step is performed by compressing the edges under a degree of pressure necessary to create cold flow of the metal, sufficient to seal and bond the periphery thereof.

[ 51 June 5, 1973 Primary Examiner.1ohn Adee Attorney John R. Benefiel[57] ABSTRACT A filter arrangement for a method of molten polymerprocessing is disclosed in which a plurality of filter elements aredisposed in a filter cavity, with each element including filter surfacesaligned with the general direction of flow through the filter cavity, tothereby increase the effective filter surface area, and each elementalso including restrictive flow paths internally of the filter surfaceto maintain a relatively large pressure drop across the filter requiredfor proper polymer processing FILTER FOR POLYMER PROCESSING AND METHODOF MANUFACTURE Inventor: Walter Kasten, Franklin, Mich.

The Bendix Corporation, Southfield,

Mich.

Filed: Aug. 21, 1972 Appl. No.: 282,088

Related U.S. Application Data [63] Continuation of Ser. No. 67,113, Aug.26, 1970 abandoned.

United States Patent 1 Kasten [73] Assignee:

in which conditioning of the molten polymer occurs to create long linkmolecules.

The method of manufacture includes the steps of assembling a sandwich ofouter layers of a filtering mesh and inner layers of a coarser mesh,diffusion bonding the layers together, sealing the edges, cutting theresulting sandwich in half by an electro-discharge, electron beam, lasermachining, or other suitable process, pressing the open edge of eachhalf into a [52] U.S. Cl. [51] Int. Cl. [58] Field ofSearch......................

In a preferred version of the 5 Claims, 7 Drawing Figures respectiveopening in a manifold plate, and'bonding each half thereto.

process, the sealing step is performed by compressing the edges under adegree of pressure necessary to create cold flow of the metal,sufficient to seal and bond the periphery thereof.

7 22.22 2222. zazz 2 2 creek v2 ...2lO/499 .....210/346 .....210/489 X ez 2 new a z 310, DIG. 15; 55/525, 526; 29/1635 References Cited UNITEDSTATES PATENTS 547 7/1947 Behlen 305 5/1951 Benedict 122 5/1957 Munch etal... 176 1/1959 154 1/1941 Anderson et a1. 1/1962 Hambrecht et al...474 7/1966 Parker et 45 7 Patented June 5, 1973 2 Sheets-Sheet 1INVENTOR WW Q4 Y B II N\ M Patented June 5, 195 3- 2 Sheets-Sheet 2 plnuniun ll I 2 1 4 A o 75222 a v 2 at TEP STEP 2 FIG? 1 STEP 4 STE/ 5INVENTOR WALTER KASTEN W /2 ATTORNEY FILTER FOR POLYMER PROCESSING ANDMETHOD OF MANUFACTURE This is a continuation of application Ser. No.67,1 13, filed Aug. 26, 1970, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionconcerns filters and more specifically filters especially adapted foruse in polymer processing operations.

2. Description of the Prior Art In processing polymers such as are usedin the manufacture of synthetic textile fibers, combination stackedmetal screen and sand pack filters are used immediately upstream of thespinnerettes to remove solid contaminants from the molten polymer whichif occluded in the extruded fiber will substantially weaken it possiblycausing it to part.

This filter pack is also used to condition the polymer, as it has beenfound that passing it through a tortuous or restrictive path under asufficiently high pressure differential encourages the formation of longlink molecules rather than closed link molecules therein, in turncontributing to improved fiber strength.

The metal screen and sand filter arrangement, however, suffers fromseveral disadvantages, the primary one being that since the contaminantdeposits on the topmost layers of the screen and sandpack, pack lifebefore pressure losses thereacross become excessive is short, on theorder of three days for a typical installation.

Another disadvantage is the high cost of servicing these units, which isthe result of the need for trained personnel to perform the assembly ofthe filter pack in the filter cavity, the separate screens and sandpacksbeing emplaced individually therein.

The solution to the service life problem is aggravated by need for theconditioning function performed by the filter pack: If a simple increasein cross section area of the filters is attempted, the time of residencein the filter increases, and the rate of movement of the molten polymerthrough the interstices declines, to the point that the conditioningprocess no longer occurs.

Therefore, it is an object of the present invention to provide aneffective filter which has a relatively long service life and acrosswhich a relatively high pressure differential occurs during thefiltering action, sufficient to condition polymers in the mannerdescribed, and a process of filtering and conditioning molten polymersusing such a filter.

It is a further object to provide such a filter which is readily andquickly emplaced by unskilled labor.

Yet another object is to provide a method of manufacturing the filterelement used in the filter of the present invention.

SUMMARY OF THE INVENTION These objects and others which will becomeapparent upon a reading of the following specification and claims isaccomplished by providing a plurality of filtering elements disposed ina filter cavity, each filter element composed of an outer layer of aporous filter mesh extending over one or more inner layers of mesh toform a sandwich, each of the filtering elements so formed disposed in amanifold plate with an open thin edge communicating with the'outlet andits major surface area disposed aligned with the general direction ofthe flow in order to provide a large effective filtering area, while atthe same time yielding a relatively large pressure drop thereacrosssince the fiow path through the filter element to the outlet is throughthe relatively thin cross section of the core, and also as a result ofthe restrictive effect of the core mesh on flow.

The method of manufacture includes the steps of assembling the layers ofouter andinner mesh, bonding them together by sealing the entireouter'edge of the assembly, cutting the assembly in half by means of anelectro-discharge, laser beam, or electron beam, and pressing the cutedge of each half into a manifold plate with a subsequent bondingthereto. In a'preferred version of the sealing step, compression of theedges sufficient to cause cold flow of the metal is used to bond andseal the edges.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially sectional viewof a typical installation of a filter assembly according to the presentinvention, together with a schematic representation of the associatedpolymer processing equipment.

FIG. 2 is a detailed view of the filter assembly depicted in FIG. 1.

FIG. 3 is a view in the direction ofline 3-3 of the DETAILED DESCRIPTIONIn the following detailed description, certain specific terminology willbe utilized for the sake of clarity and a specific embodiment describedin order to provide a complete understanding of the invention, but theinvention is not so limited and may be carried out in a variety of formsand embodiments.

Referring to the drawings, and particularly FIG. 1, the filter assembly10 is depicted, located in a filter cavity 12 in a filter housing 14.The cavity 12 is located downstream of the source of the molten polymer16 and upstream of the spinnerettes depicted schematically at 18. Thepolymer passes into the filter cavity 12, is filtered and conditioned bythe filter assembly 10, and passes out the outlet openings 20 in the endwall 22 of the housing 14, to be carried to the spinnerettes 18, wherethe fibers are formed from the molten polymer.

In order to provide an initial seal before the system is pressurized, acompression spring 21 is provided, biasing the filter assembly 10against the end wall 22, to compress a metal o-ring seal 23.

Referring to FIGS. 2-6, the filter assembly 10 is shown apart from thehousing 14, and includes a manifold plate 24 and a plurality of filterelements 26 mounted thereto.

As shown in detail in FIG. 6, each filter element 26 is composed of anouter porous filtering layer 28 on each'side, and an inner core 30 builtup of a number of layers of coarser mesh 32, with. the resultingsandwich sealed around the three outer edges at 34, by crimping,welding, sealing, or some other suitable process.

The porous outer layer 28 performs the filtering function, and hencemust be of suitable material and size for the particular application. Ina typical installation in a polymer processing situation an 165 X 800stainless mesh, 0.008 inches thick with 17 micron openings was selected.Mesh of this and other similar suitable configurations are availablecommercially, and hence it is not felt necessary to describe it indetail.

The inner core 30 in conjunction with the filter layer 28 performs thepolymer conditioning process by restricting the flow path defined by thetwo outer layers sufficiently to create the necessary minimum pressuredrop thereacross, and hence the nature and configuration of the membersmaking up the core 30 must be properly selected for each application.

For-an actual application, in which a 1,600 psi minimum and 2,500 psipressure drop maximum were required, a sandwich composed of two outer 60X 60 screens 38, 0.015 inches thick and two inner 12 X 64 screens 40(turned 90' to each other), 0.040 inches thick, yielded the necessarypressure drop characteristic.

The main core 30 also services the structural purposes of backing up thefilter layer 28 and stiffening the filter element 26 for assembly intothe manifold plate 24.

Each filter element 26 is pressed into a respective groove 42 cut acrossa raised portion 44 with each of the grooves arced downwardly into thebase portion 46 to intercept one or the other or both of an outerannular outlet groove 48 or an inner outlet opening 50, so that the openbottom portion 52 of all of the filter elements 26 communicate with oneor the other of these.

The annular outlet groove 48 and the outlet opening 50 in turn arearranged to register with the openings 20 in the filter housing 20 so asto complete the fluid circuit through the cavity 12.

In operation, the molten polymer enters the filter cavity 12, passesaround and into the filter elements 26, through the inner core 30 intothe grooves 42, and thence to the outlet groove 48 or opening 50 andfinally to the outlets 20.

Since the outlet layers 28 are of a finer mesh than those composing thecore 30, the contaminant is collected on the surface of the outer layers28 while the polymer is conditioned by the combined restrictive effectof the outer layers 28 and the inner core 30.

The disposition of the major areas of filter parallel or aligned to thedirection of flow through the cavity 12 increases theeffective area manytimes, and for one particular application, the available filter area wasincreased from approximately 3 inches square to over 30 inches square.

At the same-time, the area of the flow path through the filter cavity asa whole is not increased thereby, and thus, in combination with thesubstantial restrictive effect of the core 30, conditioning of thepolymer will still occur.

In connection with this, it is noted that the polymer will flow into thecore area up and down the height of each element 26, and the pressuredrop across the element will be an average of that occurring at thelowermost portion and the topmost portion, and in order to fullycondition the polymer without creating an excessive pressure drop, thesevalues should be within minimum and maximum range allowed in theparticular application.

Since the filtering action takes place on the surface of the filterelement 26, the assembly is readily cleaned for reuse, and as the filterassembly 10 is a unitary structure it may be easilyreplaced by unskilledlabor, hence contributing to lowered maintenance and service COStS.

From the above description of the operation of the device, it can beseen that the filtering and conditioning functions, while stillperformed by a single element, are performed in two different modes offlow: the filtering action takes place during flow through the outerfilter layer, all about the relatively large area of the surfacethereof, while the conditioning mode takes place primarily during themode of flow downward through the core, a relatively small area.

This is contrasted to the prior art discussed above, in which both thefiltering and conditioning action took place in the same mode of flowwith the inherent problem of how to increase the filter surface area toincrease service life without reducing the pressure differentialthereacross for a given flow rate to a value below the minimum necessaryfor successful conditioning.

Referring to FIG. 7, a process of manufacturing the filter element 26 isdepicted schematically. In step 1, the various layers are assembled toform a sandwich trimmed to size, and then diffusion bonded together.

In step 2, the edges are sealed about the entire periphery by a suitableprocess, i.e., welding, sealing by soldering, brazing, etc.,sufficiently to withstand the pressure differential expected to beexperienced by the element.

In connection with this last step, it has been found that compressingthe outer edges of the sandwich under sufficient pressure, cold flow ofthe metal will occur, filling the interstices, bonding and sealing theedge thereof, without the need for welding, brazing or cementing. Thiseffect is depicted in the filter elements shown in FIG. 6. This approachwill produce a sound bond at a low cost, and is susceptible to highvolume production methods involving die forming of the peripheral edges.

In step 3, the sandwich is severed in half, preferably by anelectro-discharge machine, so that burring and crushing of the edges isminimized, and flow through the resulting opening will be substantiallyunhindered. Alternatively, an electron beam or laser machining processcould be used.

In step 4, the cut edge is compressed slightlyand in step 5, each halfportion is press fitted into a respective slightly undersized slot inthe manifold plate, and subsequently secured thereto by diffusionbonding, welding, etc., so that the joint is capable of withstanding theexpected pressure differential without leakage.

As can be readily appreciated, this method provides an efficient andexpeditious construction ofthe individual filter elements withoutwastage.

While a specific embodiment has been described in order to provide amore complete understanding of the invention, many variations thereofare possible within the scope of the invention. Forl example, the flatsandwich type of configuration of the filter element shown, while apreferred configu-ration, could be modified to a cylindrical or othersuch shape while retaining its ess'ential characteristic. Furthermore,the construction of the core, i.e., a built-up sandwich, could be variedto provide an alternate restrictive flow path such as a porous unitaryelement, of the proper configuration.

Finally, the filter assembly, while offering particular and substantialadvantages in the context of polymer processing, could be used in anyother context in which a relatively large pressure drop across a largeeffective area filter is desired.

What is claimed is:

l. A method of manufacturing a filter element comprising the steps of:

assembling lower and upper filter layers with at least one layer of meshin between;

sealing the resulting sandwich about its periphery;

cutting the sandwich into sections having at least one unsealed edge;

pressing the unsealed edge of each portion into a slot- 4 ted manifoldplate.

2. The method of claim 1 wherein the cutting step includeselectro-discharge severing of the sandwich, whereby a smooth opening forflow through the opening formed by said cutting step is provided.

3. The method of claim 1 wherein the sealing step includes the step ofcompressing the outer edges of said sandwich to cause cold flow of thefilter layer and mesh material to thereby substantially seal theperiphery of said sandwich.

4. A process of filtering and conditioning molten polymer material priorto fiber spinning comprising the steps of:

filtering the molten polymer by passing it through an outer porousfiltering layer;

conditioning the molten polymer to create formation of long linkmolecules by subsequently passing the molten polymer through arestrictive flow path, enclosed at least in part by said outer porousfiltering layer and in a direction wherein the flow path cross-sectionalarea is substantially less than that of the outer porous filtering layerfiltering area, whereby filtering is carried out in a substantiallylarger flow area than the condi-tioning occurring in said restrictiveflow path while both are carried out within the space occupied by saidouter porous filtering layer.

5. The method of claim 4 wherein in said subsequent passing step saidpolymer is passed through a core element surrounded by said porousfiltering layer so as to be disposed in said flow path and havingnumerous openings therein coarser than said outer porous filtering layerpores, whereby filtering takes place solely on the outer surface of saidouter porous filtering layer.

2. The method of claim 1 wherein the cutting step includeselectro-discHarge severing of the sandwich, whereby a smooth opening forflow through the opening formed by said cutting step is provided.
 3. Themethod of claim 1 wherein the sealing step includes the step ofcompressing the outer edges of said sandwich to cause cold flow of thefilter layer and mesh material to thereby substantially seal theperiphery of said sandwich.
 4. A process of filtering and conditioningmolten polymer material prior to fiber spinning comprising the steps of:filtering the molten polymer by passing it through an outer porousfiltering layer; conditioning the molten polymer to create formation oflong link molecules by subsequently passing the molten polymer through arestrictive flow path, enclosed at least in part by said outer porousfiltering layer and in a direction wherein the flow path cross-sectionalarea is substantially less than that of the outer porous filtering layerfiltering area, whereby filtering is carried out in a substantiallylarger flow area than the condi-tioning occurring in said restrictiveflow path while both are carried out within the space occupied by saidouter porous filtering layer.
 5. The method of claim 4 wherein in saidsubsequent passing step said polymer is passed through a core elementsurrounded by said porous filtering layer so as to be disposed in saidflow path and having numerous openings therein coarser than said outerporous filtering layer pores, whereby filtering takes place solely onthe outer surface of said outer porous filtering layer.